過去の記録

過去の記録 ~11/11本日 11/12 | 今後の予定 11/13~

2018年12月19日(水)

作用素環セミナー

16:45-18:15   数理科学研究科棟(駒場) 126号室
水田黎 氏 (東大数理)
Polynomial Time Algorithm for Computing N-th Moments of a Self-Adjoint Operator in Algebra Generated by Free Independent Semicircular Elements

代数学コロキウム

17:30-18:30   数理科学研究科棟(駒場) 056号室
Jean-Stefan Koskivirta 氏 (東京大学数理科学研究科)
Cohomology vanishing for automorphic vector bundles (ENGLISH)
[ 講演概要 ]
A Shimura variety carries naturally a family of vector bundles parametrized by the characters of a maximal torus in the attached group. We want to determine which of these vector bundles are ample, and also show cohomology vanishing results. For this we use generalized Hasse invariants on the stack of G-zips of Moonen-Pink-Wedhorn-Ziegler. It is a group-theoretical counterpart of the Shimura variety and carries a similar family of vector bundles. This is joint work with Y.Brunebarbe, W.Goldring and B.Stroh.

2018年12月18日(火)

PDE実解析研究会

10:30-11:30   数理科学研究科棟(駒場) 056号室
In-Jee Jeong 氏 (Korea Institute for Advanced Study (KIAS))
Dynamics of singular vortex patches (English)
[ 講演概要 ]
Vortex patches are solutions to the 2D Euler equations that are given by the characteristic function of a bounded domain that moves with time. It is well-known that if initially the boundary of the domain is smooth, the boundary remains smooth for all time. On the other hand, we consider patches with corner singularities. It turns out that, depending on whether the initial patch satisfies an appropriate rotational symmetry condition or not, the corner structure may propagate for all time or lost immediately. In the rotationally symmetric case, we are able to construct patches with interesting dynamical behavior as time goes to infinity. When the symmetry is absent, we present a simple yet formal evolution equation which describes the dynamics of the boundary. It suggests that the angle cusps instantaneously for $t > 0$.
This is joint work with Tarek Elgindi.

トポロジー火曜セミナー

17:30-18:30   数理科学研究科棟(駒場) 056号室
Tea: Common Room 17:00-17:30
鳥居 猛 氏 (岡山大学)
離散GスペクトラムとK(n)局所安定ホモトピー圏のモデルについて (JAPANESE)
[ 講演概要 ]
K(n)局所安定ホモトピー圏はスペクトラムの安定ホモトピー圏の基本構成単位と考えられる。この講演ではMorava E理論とその安定化群との関係が明確になるようなK(n)局所安定ホモトピー圏のモデルを構成する。そのために、Behrens-Davisにより研究された副有限群Gに対する離散対称Gスペクトラムについて考える。そして、K(n)局所安定ホモトピー圏が、離散対称G_nスペクトラムの圏におけるE_nの離散モデル上の加群のホモトピー圏の中に実現されることを示す。

2018年12月17日(月)

複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室
神本丈 氏 (九州大学)
Newton polyhedra and order of contact on real hypersurfaces (JAPANESE)
[ 講演概要 ]
This talk will concern some issues on order of contact on real hypersurfaces, which was introduced by D'Angelo. To be more precise, a sufficient condition for the equality of regular type and singular type is given. This condition is written by using the Newton polyhedron of a defining function. Our result includes earlier known results concerning convex domains, pseudoconvex Reinhardt domains and pseudoconvex domains whose regular types are 4. Furthermore, under the above condition, the values of the types can be directly seen in a simple geometrical information from the Newton polyhedron.

The technique of using Newton polyhedra has many significant applications in singularity theory. In particular, this technique has been great success in the study of the Lojasiewicz exponent. Our study about the types is analogous to some works on the Lojasiewicz exponent.

2018年12月14日(金)

代数幾何学セミナー

10:30-11:30   数理科学研究科棟(駒場) 123号室
Zhi Jiang 氏 (Fudan)
On the birationality of quint-canonical systems of irregular threefolds of general type (English)
[ 講演概要 ]
It is well-known that the quint-canonical map of a surface of general type is birational.
We will show that the same result holds for irregular threefolds of general type. The proof is based on
a careful study of the positivity of the pushforwards of pluricanonical bundles on abelian varieties and Severi
type inequalities. This is a joint work with J.A. Chen, J.Chen, and M.Chen.

2018年12月12日(水)

代数学コロキウム

18:00-19:00   数理科学研究科棟(駒場) 056号室
Gaëtan Chenevier 氏 (CNRS, Université Paris-Sud)
A higher weight (and automorphic) generalization of the Hermite-Minkowski theorem (ENGLISH)
[ 講演概要 ]
I will show that for any integer N, there are only finitely many cuspidal algebraic automorphic representations of GL_m over Q whose Artin conductor is N and whose "weights" are in the interval {0,...,23} (with m varying). Via the conjectural yoga between geometric Galois representations (or motives) and algebraic automorphic forms, this statement may be viewed as a generalization of the classical Hermite-Minkowski theorem in algebraic number theory. I will also discuss variants of these results when the base field Q is replaced by an arbitrary number field.

(本講演は「東京北京パリ数論幾何セミナー」として,インターネットによる東大数理,Morningside Center of Mathematics と IHES の双方向同時中継で行います.今回はパリからの中継です.)

2018年12月11日(火)

PDE実解析研究会

10:30-11:30   数理科学研究科棟(駒場) 056号室
Marek Fila 氏 (Comenius University in Bratislava)
Solutions with moving singularities for equations of porous medium type (English)
[ 講演概要 ]
We construct positive solutions of equations of porous medium type with a singularity which moves in time along a prescribed curve and keeps the spatial profile of singular stationary solutions. It turns out that there appears a critical exponent for the existence of such solutions. This is a joint work with Jin Takahashi and Eiji Yanagida.

トポロジー火曜セミナー

17:30-18:30   数理科学研究科棟(駒場) 056号室
Tea: Common Room 17:00-17:30
石田 政司 氏 (大阪大学)
On non-singular solutions to the normalized Ricci flow on four-manifolds (JAPANESE)
[ 講演概要 ]
A solution to the normalized Ricci flow is called non-singular if the solution exists for all time and the Riemannian curvature tensor is uniformly bounded. In 1999, Richard Hamilton introduced it as an important special class of solutions and proved that the underlying 3-manifold is geometrizable in the sense of Thurston. In this talk, we will discuss properties of 4-dimensional non-singular solutions from a gauge theoretical point of view. In particular, we would like to explain gauge theoretical invariants give rise to obstructions to the existence of 4-dimensional non-singular solutions.

Lie群論・表現論セミナー

17:00-18:00   数理科学研究科棟(駒場) 117号室
滝聞太基 氏 (東京大学大学院数理科学研究科)
A Pieri-type formula and a factorization formula for K-k-Schur functions
[ 講演概要 ]
We give a Pieri-type formula for the sum of K-k-Schur functions \sum_{\mu\le\lambda}g^{(k)}_{\mu} over a principal order ideal of the poset of k-bounded partitions under the strong Bruhat order, which sum we denote by \widetilde{g}^{(k)}_{\lambda}. As an application of this, we also give a k-rectangle factorization formula \widetilde{g}^{(k)}_{R_t\cup\lambda}=\widetilde{g}^{(k)}_{R_t} \widetilde{g}^{(k)}_{\lambda}
where R_t=(t^{k+1-t}), analogous to that of k-Schur functions s^{(k)}_{R_t\cup \lambda}=s^{(k)}_{R_t}s^{(k)}_{\lambda}.

2018年12月10日(月)

東京確率論セミナー

17:00-18:00   数理科学研究科棟(駒場) 号室
東京工業大学(大岡山) 本館 H112講義室での開催となります(いつもと時間・場所が異なりますのでご注意ください). 主催 :東京工業大学 量子物理学・ナノサイエンス先端研究センター
Nikolaos Zygouras 氏 (University of Warwick)
Random polymer models and classical groups (ENGLISH)
[ 講演概要 ]
The relation between polymer models at zero temperature and characters of the general linear group GL_n(R) has been known since the first breakthroughs in the field around the KPZ universality through the works of Johansson, Baik, Rains, Okounkov and others. Later on, geometric liftings of the GL_n(R) characters appeared in the study of positive temperature polymer models in the form of GL_n(R)-Whittaker functions. In this talk I will describe joint works with E. Bisi where we have established that Whittaker functions associated to the orthogonal group SO_{2n+1}(R) can be used to describe laws of positive temperature polymers when their end point is free to lie on a line. Going back to zero temperature, we will also see that characters of other classical groups such as SO_{2n+1}(R); Sp_{2n}(R); SO_{2n}(R) do play a role in describing laws of polymers in various geometries. This occurence might be surprising given the length of time these models have been studied.
[ 講演参考URL ]
https://warwick.ac.uk/fac/sci/statistics/staff/academic-research/zygouras/

2018年12月07日(金)

作用素環セミナー

15:00-17:00   数理科学研究科棟(駒場) 002号室
戸松玲治 氏 (北海道大学)
従順C*テンソル圏のvon Neumann環への中心的自由作用について (5)

2018年12月06日(木)

東京無限可積分系セミナー

16:00-17:00   数理科学研究科棟(駒場) 002号室
Francesco Ravanini 氏 (University of Bologna)
Integrability and TBA in non-equilibrium emergent hydrodynamics (ENGLISH)
[ 講演概要 ]
The paradigm of investigating non-equilibrium phenomena by considering stationary states of emergent hydrodynamics has attracted a lot of attention in the last years. Recent proposals of an exact approach in integrable cases, making use of TBA techniques, are presented and discussed.

作用素環セミナー

15:00-17:00   数理科学研究科棟(駒場) 128号室
戸松玲治 氏 (北海道大学)
従順C*テンソル圏のvon Neumann環への中心的自由作用について (4)

2018年12月05日(水)

作用素環セミナー

17:15-18:45   数理科学研究科棟(駒場) 126号室
Frederic Latremoliere 氏 (Univ. Denver)
The Gromov-Hausdorff Propinquity

作用素環セミナー

15:00-17:00   数理科学研究科棟(駒場) 002号室
戸松玲治 氏 (北海道大学)
従順C*テンソル圏のvon Neumann環への中心的自由作用について (3)

統計数学セミナー

13:00-15:00   数理科学研究科棟(駒場) 156号室
Yuliia Mishura 氏 (The Taras Shevchenko National University of Kiev)
Lecture 2:Representation results for the Gaussian processes. Financial applications of fractional Brownian motion

[ 講演概要 ]
Arbitrage with fBm: why it appears. How to present any contingent claim via self-financing strategy on the financial market involving fBm. Absence of arbitrage for the mixed models. Fractional -Uhlenbeck and fractional Cox-Ingersoll-Ross processes as the models for stochastic volatility.

統計数学セミナー

15:00-17:00   数理科学研究科棟(駒場) 156号室
Yuliia Mishura 氏 (The Taras Shevchenko National University of Kiev)
Lecture 3:Statistical parameter estimation for the diffusion processes and in the models involving fBm

[ 講演概要 ]
Drift parameter estimation in the standard diffusion model and its strong consistency. Hurst and drift parameter estimation in the models involving fBm and in the mixed models. Asymptotic properties. Estimation of the diffusion parameter.

2018年12月04日(火)

トポロジー火曜セミナー

17:00-18:30   数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
Vincent Florens 氏 (Université de Pau et des Pays de l'Adour)
Slopes and concordance of links (ENGLISH)
[ 講演概要 ]
We define the slope of a link associated to admissible characters on the link group. Away from a certain singular locus, the slope is a rational function which can be regarded as a multivariate generalization of the Kojima-Yamasaki η-function. It is the ratio of two Conway potentials, provided that the latter makes sense; otherwise, it is a new invariant. We present several examples and discuss the invariance by concordance. Joint with A. Degtyarev and A. Lecuona.

作用素環セミナー

15:00-17:00   数理科学研究科棟(駒場) 002号室
戸松玲治 氏 (北海道大学)
従順C*テンソル圏のvon Neumann環への中心的自由作用について (2)

統計数学セミナー

15:00-17:00   数理科学研究科棟(駒場) 126号室
Yuliia Mishura 氏 (The Taras Shevchenko National University of Kiev)
Lecture 1: Elements of fractional calculus
How to connect the fractional Brownian motion to the Wiener process. Stochastic integration w.r.t. fBm and stochastic differential equations involving fB
[ 講演概要 ]
Fractional integrals and fractional derivatives. Wiener and stochastic integration w.r.t. the fractional Brownian motion. Representations of fBm via a Wiener process and vice versa. Elements of the fractional stochastic calculus. Stochastic differential equations involving fBm: existence, uniqueness, properties of the solutions. Simplest models: fractional Ornstein-Uhlenbeck and fractional Cox-Ingersoll-Ross processes.

2018年12月03日(月)

作用素環セミナー

15:00-17:00   数理科学研究科棟(駒場) 002号室
戸松玲治 氏 (北海道大学)
従順C*テンソル圏のvon Neumann環への中心的自由作用について (1)

複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室
細野元気 氏 (東京大学)
多変数関数論における変動理論 (JAPANESE)
[ 講演概要 ]
関数論において、領域の擬凸変動に関する様々な量の劣調和性が知られている。例えば、山口によるRobin定数の変動、米谷-山口によるBergman核の変動が知られている。また、Bergman核の変動理論のある種の一般化として、Berndtssonにより、$L^2$正則関数のなす空間の変動に関する正曲率性が知られている。これらの理論は$L^2$拡張定理とも深い関係が知られており、その意味でも興味深い。本講演では、これらの理論に関して知られている結果を紹介し、Robin定数の変動問題の多変数化として東川擬距離の変動問題についての考察を行う。

Lie群論・表現論セミナー

17:00-18:00   数理科学研究科棟(駒場) 126号室
Ali Baklouti 氏 (Sfax 大学)
Monomial representations of discrete type and differential operators. (English)
[ 講演概要 ]
Let $G$ be an exponential solvable Lie group and $\tau$ a monomial representation of $G$, an induced representation from a connected closed subgroup of $G$ of a unitary character. It is well known that $\tau$ disintegrates into irreducible factors and the multiplicities of each isotypic component are explicitly determined. In the case where $G$ is nilpotent, these multiplicities are either finite or infinite almost everywhere, with respect to the disintegration's measure. We associate to $\tau$ an algebra of differential operators and it is shown that in the nilpotent case, the commutativity of this algebra is equivalent to the finiteness of the multiplicities of $\tau$. In the exponential case, we define the notion of monomial representation of discrete type. In this case, we show that such an equivalence does not hold and this answers a question posed by M. Duflo. This is a joint work with H. Fujiwara and J. Ludwig.

2018年11月30日(金)

談話会・数理科学講演会

15:30-16:30   数理科学研究科棟(駒場) 002号室
三竹大寿 氏 (東京大学大学院数理科学研究科)
粘性解理論とAubry-Mather理論 (日本語)
[ 講演概要 ]
力学系におけるAubry-Mather理論は,偏微分方程式論の粘性解理論を導入することで相互の理論がより明瞭なものとなった.この理論は,Kolmogorov-Arnold-Moser (KAM) 理論を背景に偏微分方程式論における弱解を利用した理論ということで,弱KAM 理論と提唱された.講演者は,最適確率制御問題に現れる退化粘性HJ方程式と呼ばれるクラスの方程式に適用できるよう,弱KAM理論の一般化に取り組んできた.従来の弱KAM理論は決定論的な力学系しか扱えないため,新しい道具立てを必要とした.この点を偏微分方程式論から見直すことで決定論及び確率論を統一する一つの新しい枠組みを作ることに成功してきた.その応用として,漸近解析(長時間挙動,ディスカウント近似)ついて解決した.本講演では,関連した内容について,次の2点に焦点をおいて話す.

(i) 非線形随伴法を利用した漸近解析:非線形随伴法を利用した漸近解析として,退化粘性HJ方程式の長時間挙動,ディスカウント近似の極限に関する結果について紹介する.
(ii) 均質化問題の解の収束率 :HJ方程式の均質化問題は,1987年にLions,Papanicolaou, Varadhanによる有名な未発表論文により提唱された後,劇的に研究が進展し,大多数の論文が発表された.しかし,PDE的手法だけでは収束率について得ることは難しかった.本講演では,Aubry-Mather理論の観点から問題を見直すことで得られた収束率の結果について紹介する.

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